The present invention relates generally to ultrasonic imaging catheters, and more particularly, to catheters having improved electrical connections for ultrasonic transducers.
Intravascular imaging of blood vessels and surrounding tissues continues to be of great benefit in a wide range of medical fields. A particularly successful design for an intravascular imaging catheter employs a rotatable imaging assembly containing an ultrasonic transducer, where the assembly is attached to the distal end of a flexible drive cable. The transducer may be rotated within a catheter body or sheath in order to transmit an ultrasonic signal and produce a video image by well-known techniques. The transducer element or elements are connected to electronics, typically maintained outside the patient""s body, to produce the video image.
To connect the transducer to the electronics, an electrode or lead typically is physically attached to either the transducer face or to the face of a matching layer which is, in turn, attached to the transducer face. However, such an attachment (e.g., a conductive silver epoxy soldered attachment point) can adversely affect the transmission and receipt of ultrasonic signals by the transducer. In short, the attachment interferes with or blocks at least part of the transmitted and/or reflected signals. This problem is further exacerbated by the fact that such attachments often are made by hand. Attachments made by hand typically vary in both size and location from catheter to catheter. As a result, it can be difficult to predict the amount of interference the attachment will produce for a particular imaging catheter.
Further, when a sound wave generated by a typical transducer impinges on an interface between two different media, such as the interface between the transducer face and the tissue being imaged, part of the incident wave is reflected and part is transmitted. The amount of wave reflected compared to the amount transmitted depends primarily on the relative acoustic impedances of the two media. In general, it is desirable to reduce or minimize the difference in acoustic impedance between the two media to permit a greater amount of the wave energy to transmit through the interface. Some existing catheters attach one or more matching layers to the transducer face which have an acoustic impedance between that of the transducer and that of the tissue being imaged. It is desirable, and a further object of the present invention, to provide a method of tuning the matching layer to have a desired acoustic impedance when coupled to the transducer.
The present invention provides ultrasound transducer packages having off-aperture electrical connections, imaging assemblies employing such packages, and methods of making same. The transducer packages of the present invention are intended to overcome at least some of the problems of the prior art. For example, the present invention moves the electrode or front lead attachment off-aperture, or off the transducer face. This reduces or eliminates the interference such attachment points may cause to the ultrasound signals transmitted from and/or received by the transducer element. Further, imaging assemblies of the present invention are designed to have matching layers that can be tuned to improve impedance matching. Such assemblies are hence more uniform and predictable, and have improved performance.
In one embodiment, the present invention provides a transducer package for an imaging catheter. The transducer package includes a transducer element and a matching layer operably attached to the transducer element to create an overhang portion of the matching layer. A lead is operably attached to the overhang portion. In this manner, signals can be sent from, and received by, the transducer by establishing an electrical connection with the overhang portion via the lead. Preferably, this lead also is attached to an electrical signal source to send electrical signals to the transducer element for ultrasound imaging. The electrical connection is made with a reduced concern as to the size or precise location of the attachment point because the lead or other electrical connection device is attached to the overhang portion of the matching layer and not to the transducer or to the non-overhanging portion of the matching layer face.
Other exemplary off-aperture connection apparatus and methods are disclosed in U.S. Pat. No. 6,036,647, entitled xe2x80x9cPZT Off-Aperture Bonding Techniquexe2x80x9d; U.S. patent application Ser. No. 09/127,089, entitled xe2x80x9cOff-Aperture Electrical Connection for Ultrasonic Transducerxe2x80x9d; and U.S. Pat. No. 6,162,178, entitled xe2x80x9cUltrasonic Transducer Off-Aperture Connectionxe2x80x9d, the complete disclosures of which are incorporated herein by reference.
In one aspect, the transducer element has first and second spaced apart surfaces, with the first surface having a first area. The matching layer has third and fourth spaced apart surfaces, with the third surface having a second area. The second area is larger than the first area. The third surface is operably attached to the first surface to provide the overhang portion. In one particular aspect, the third surface completely covers the first surface and produces the overhang portion.
In another aspect, the matching layer and transducer element further include a conductive material so that operably attaching the third surface to the first surface produces an electrically conductive path therebetween. In one aspect, the transducer element is operably attached to the matching layer using an epoxy layer.
In one aspect, the matching layer includes a thermoplastic. In this manner, the thermoplastic can be conformed to the appropriate size and/or thickness in order to facilitate impedance matching between the transducer element and the matching layer, and between the matching layer and the tissue or fluid to be imaged. Alternatively, the matching layer includes an uncatalyzed epoxy, a B-stage epoxy, other modifiable materials, and the like. It will be appreciated by those skilled in the art that the matching layer may comprise additional materials within the scope of the present invention.
In another aspect, the transducer package further includes a second matching layer operably attached to the first matching layer. Preferably, the second matching layer has a different acoustic impedance than the first matching layer. For example, in some instances it is desirable for the second matching layer to have an acoustic impedance that is lower than an impedance of the first matching layer, which is in turn lower than the impedance of the transducer element. Such use of matching layer(s) is particularly desirable since transducer elements typically have a significantly higher impedance than an impedance of the surrounding tissue being imaged.
In still another aspect, the transducer package further includes a backing material operably attached to the transducer element. Backing material preferably is used to reduce or eliminate the effect of ultrasound signals propagating from, or received by, the side of the transducer element contacting the backing material. This, in turn, improves the overall performance of the transducer. In one aspect, the transducer element includes a material selected from a group of materials consisting of piezoceramics, piezocomposites, and piezoplastics.
In one particular embodiment of the present invention, a transducer package for an imaging catheter includes a transducer element and a first matching layer operably attached to the transducer element. The first matching layer includes a thermoplastic, such as a thermoplastic film, a thermoset film whose shape is deformable with heat and/or pressure, and the like. In this manner, the use of a thermoplastic matching layer facilitates the tuning of the matching layer to have desired acoustic impedance properties. Additionally, the use of thermoplastics facilitates the use of a curved matching layer with, for example, a transducer element having a curved surface. For example, in one aspect, the transducer element has a first curved surface and the first matching layer has a second curved surface. The transducer element and first matching layer are operably attached so that the first and second curved surfaces are coupled.
Additional uses of curved matching layer and transducer element surfaces are disclosed in U.S. Pat. No. 6,287,261, entitled xe2x80x9cFocused Ultrasound Transducer and Systemsxe2x80x9d, the complete disclosure of which is incorporated herein by reference. Additional tuning methods and advantages are disclosed in U.S. patent application Ser. No. 09/127,694, entitled xe2x80x9cMethod of Tuning Ultrasonic Transducer Matching Layerxe2x80x9d now abandoned, the complete disclosure of which is incorporated herein by reference.
In one aspect of the embodiment, the first matching layer is operably attached to the transducer element to create an overhang portion of the first matching layer. In one particular aspect, the transducer package further includes a lead operably attached to the overhang portion. Alternatively, the transducer package further includes a second matching layer operably attached to the first matching layer, preferably in a manner which creates an overhang portion of the second matching layer. The lead again is operably attached to the overhang portion.
The invention further provides an exemplary imaging assembly, which includes a housing having a distal end, a proximal end and a longitudinal axis. A transducer package is operably attached to the housing distal end. The transducer package includes a transducer element, a matching layer, preferably comprising a thermoplastic, operably attached to the transducer element to create an overhang portion of the matching layer, and a lead operably attached to the overhang portion. Preferably, the imaging assembly further includes a drive cable operably attached to the housing proximal end. In this manner, the drive cable rotates the imaging assembly to rotate the transducer package, for example, during ultrasound imaging.
The present invention further provides exemplary methods of making a transducer package. One particular method includes the step of providing a transducer element having first and second electrodes operably attached to first and second transducer element surfaces, respectively. A matching layer is provided having at least one electrically conductive surface. The transducer element and matching layer conductive surface are coupled together with an adhesive layer to produce an electrically conductive path between the first electrode and the matching layer conductive surface. The coupling step further creates an overhang portion of the matching layer. The method includes attaching a lead to the overhang portion. In one aspect of the method, the adhesive layer includes an electrically non-conductive epoxy layer. Other adhesives may be used within the scope of the present invention, including conductive epoxy or adhesive layers.
In one particular aspect, the matching layer includes a thermoplastic. The coupling step includes compressing the matching layer and transducer element together using a desired pressure and a desired temperature. The method includes reducing the temperature after the matching layer and transducer element have been compressed into a desired shape and/or thickness, and thereafter reducing the pressure so that the matching layer and transducer element retain the desired shape and/or thickness. In this manner, characteristics of thermoplastics are used to form the matching layer into a desired shape and/or thickness, thereby tuning the matching layer to the desired acoustic impedance, and shaping if desired. For example, in one aspect, the matching layer and transducer element have a desired radius of curvature when in the desired shape.
Other features and advantages of the invention will appear from the following description in which the preferred embodiment has been set forth in detail in conjunction with the accompanying drawings.